1. Field of the Invention
The invention relates generally to vehicular air conditioning apparatus. More particularly, the invention relates to circuits for driving compressor motors of vehicular air conditioning apparatus.
2. Description of Related Art
Referring to FIG. 1, a known drive circuit 2 for driving a known compressor motor 100, e.g., a brushless D.C. motor, of a vehicular air conditioning apparatus, such as the drive circuit described in Japanese Patent Publication No. HEI 8-98581, is depicted. An input side of drive circuit 2 is connected to a DC power supply 1 of the air conditioning apparatus, e.g., a battery, such as a forty-two (42) Volt vehicular battery, via a switching mechanism 9 of the air conditioning apparatus, e.g., a switch. Moreover, an output side of drive circuit 2 is connected to compressor motor 100. Drive circuit 2 comprises a smoothing capacitor 30 and an inverter 3. Inverter 3 comprises a plurality of switching elements 3a, e.g., a plurality of switches, and inverter 3 and capacitor 30 are each connected to a positive terminal of DC power supply 1 via switching mechanism 9. The connection between inverter 3 and the positive terminal of DC power supply 1 via switching mechanism 9 forms a first positive electrical path 7p. Moreover, inverter 3 and capacitor 30 are each directly connected to a negative terminal of DC power supply 1. The direct connection between inverter 3 and the negative terminal of DC power supply 1 forms a first negative electrical path 7n, and a main electrical path 7 comprises first positive electrical path 7p and first negative electrical path 7n. 
Drive circuit 2 also comprises a DC to DC converter 6. A positive input of DC to DC converter 6 is connected to the positive terminal of DC power supply 1 via first positive electrical path 7p and switching mechanism 9, and a negative input of DC to DC converter 6 is connected to the negative terminal of DC power supply 1 via first negative electrical path 7n. The connection between the positive input of DC to DC converter 6 and first positive electrical path 7p forms a second positive electrical path 8p. The connection between the negative input of DC to DC converter 6 and first negative electrical path 7n forms a second negative electrical path 8n, and a secondary electrical path 8 comprises second positive electrical path 8p and second negative electrical path 8n. Drive circuit 2 also comprises a switching element circuit 4 for selectively activating, i.e., placing in a closed position, and selectively deactivating, i.e., placing in an open position, each of the plurality of switching elements 3a of inverter 3, and a feedback circuit 5 for controlling switching element circuit 4.
In operation, an operator or a passenger of a vehicle, i.e., a user of the air conditioning apparatus, may turn on an air conditioning apparatus control circuit 200, e.g., by moving a switch of air conditioning apparatus control circuit 200 from a first position to a second position, and air conditioning apparatus control circuit 200 may activate switching mechanism 9. When switching mechanism 9 is activated, i.e., when switching mechanism is in a closed position, and for so long as at least one switching element 3a of inverter 3 also is activated, the amount of current flowing through first positive electrical path 7p and first negative electrical path 7n may be about one-hundred (100) amps. In contrast, when switching mechanism 9 is deactivated, or when switching mechanism 9 is activated and each of switching elements 3a are deactivated, the amount of current flowing through first positive electrical path 7p and first negative electrical path 7n may be about zero (0) amps. Moreover, when switching mechanism 9 is activated, regardless of whether each of switching elements 3a are activated or are deactivated, i.e., regardless of whether drive circuit 2 is activated or deactivated, the amount of current flowing through second positive electrical path 8p and second negative electrical path 8n may be about twenty-four (24) milli amps.
In operation, DC to DC converter 6 may convert voltage from DC power supply 1 to a lower voltage and may deliver the converted voltage to switching element circuit 4 and feedback circuit 5. For example, when DC power supply 1 is a forty-two (42) Volt vehicular battery, DC to DC converter 6 may convert the forty-two (42) volts from DC power supply 1 into five (5) Volts, and also may deliver five (5) Volts to switching element circuit 4 and feedback circuit 5. When switching element circuit 4 and feedback circuit 5 receive the converted voltage, switching element circuit 4 and feedback circuit 5 selectively activate or deactivate switching elements 3a of inverter 3.
When at least one of switching elements 3a is activated, for so long as switching mechanism 9 is activated, current flows to compressor motor 100, such that a drive shaft (not shown) of compressor motor 100 rotates. When the drive shaft of compressor motor 100 rotates, an electromotive force signal is generated between the terminals of compressor motor 100. The electromotive force signal includes information related to the angular position of a rotor (not shown), and is delivered to feedback circuit 5, such that feedback circuit 5 may process the electromotive force signal in order to determine the angular position of the rotor. When feedback circuit 5 determines the angular position of the rotor, if the angular position of the rotor is different than a predetermined angular position, switching element circuit 4 and feedback circuit 5 change the position of at least one of switching elements 3a in order to adjust the angular position of the rotor. When the user turns air conditioning apparatus control circuit 200 off, e.g., by moving the switch of air conditioning apparatus control circuit 200 from the second position to the first position, switching mechanism 9 may be deactivated.
When switching mechanism 9 is activated and switching elements 3a are deactivated, the amount of current flowing through first positive electrical path 7p and first negative electrical path 7n may be about zero (0) amps, and the amount of current flowing through second positive electrical path 8p and second negative electrical path 8n still may be about twenty-four (24) milli amps. As such, when switching mechanism 9 is activated, the amount of current flowing through second positive electrical path 8p and second negative electrical path 8n may be about twenty-four (24) milli amps regardless of whether switching elements 3a are activated or are deactivated, i.e., regardless of whether drive circuit 2 is activated or deactivated.
Moreover, because inverter 3 is connected to the positive terminal of DC power supply 1 via switching mechanism 9, such the amount of current flowing through first positive electrical path 7p and first negative electrical path 7n may be about one-hundred (100) amps, in order to prevent damage to switching mechanism 9 during operation, switching mechanism 9 must be of a size sufficient to handle one-hundred (100) amps. Consequently, switching mechanism 9 may be a relay or a field effect transistor having an Ampere rating of at least one-hundred (100) amps. Further, because when switching mechanism 9 is activated the amount of current flowing through second positive electrical path 8p and second negative electrical path 8n may be about twenty-four (24) milli amps regardless of whether drive circuit 2 is activated or deactivated, DC power supply 1 may lose power in a short period of time.
Therefore, a need has arisen for air conditioning apparatus which overcome these and other short comings of the related art. A technical advantage of the present invention is that an air conditioning apparatus may comprise a switching mechanism having an Ampere rating of less than one-hundred (100) amps, e.g., about 25 milli amps, which reduces the cost of manufacturing the air conditioning apparatus and reduces power consumption by the air conditioning apparatus, without damaging the switching mechanism. Another technical advantage of the present invention is that a DC power supply may not lose power when a drive circuit is deactivated.
According to an embodiment of the present invention, an air conditioning apparatus is described. The air conditioning apparatus comprises a DC power supply, e.g., a battery, such as a vehicular battery, at least one switching mechanism, e.g., at least one switch, and a drive circuit. The drive circuit comprises an inverter including a plurality of switching elements, e.g., a plurality of switches. The inverter is directly connected to a positive terminal of the DC power supply and is directly connected to a negative terminal of the DC power supply. The drive circuit also comprises a DC to DC converter. In one embodiment, a positive terminal of the DC to DC converter is connected to the positive terminal of the DC power supply via the at least one switching mechanism. In another embodiment, a negative terminal of the DC to DC converter is connected to the negative terminal of the DC power supply via the at least one switching mechanism. The drive circuit also comprises a switching element circuit coupled to the inverter and to the DC to DC converter. The switching element circuit selectively activates and deactivates the plurality of switching elements. Moreover, the drive circuit comprises a feedback circuit coupled to the switching element circuit and to the DC to DC converter. The feedback circuit controls the switching element circuit in response to an angular position of a rotor.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art in view of the following detailed description of the invention and the accompanying drawings.